Synthesis gases, that is, gases that contain hydrogen and carbon monoxide are produced by steam methane reforming, autothermal reforming, partial oxidation, either catalytic or non-catalytic. The resultant synthesis gas stream can be further processed in a water gas shift reactor to increase its hydrogen content and the hydrogen can be separated from the synthesis gas to produce a hydrogen product stream though pressure swing adsorption.
Gas turbines are very commonly located at synthesis gas production sites. In this regard, commonly, the fuel for both the gas turbine and the hydrocarbon containing reactant fed for the synthesis gas production is natural gas. Where such installations exist, the gas turbines are not normally thermally linked to the synthesis gas production. In integrated gasification combined cycles, however, the gas turbine and the synthesis gas production are both thermally and operationally linked in that the fuel to the gas turbine is the synthesis gas and the synthesis gas is reheated through heat transfer with the synthesis gas stream being produced.
For example, in EP 0 575 406 B1, fuel and oxygen are reacted in a partial oxidation reactor to produce a synthesis gas stream. After the synthesis gas stream is quenched and water is removed in a knock-out drum at high temperature, the synthesis gas stream is subjected to a water gas shift reaction at a temperature of between 260° C. and 472° C. The heat created by the exothermic shift reaction is used in downstream heat exchangers to reheat the fuel stream to the gas turbine to a temperature of about 390° C. The fuel for the gas turbine is derived entirely from the synthesis stream. In this regard, in cooling stages occurring subsequent to the water gas shift, water is removed from the synthesis gas stream. After sulfur removal, the synthesis gas is reheated and, as stated previously, used as fuel to the gas turbine. As can be appreciated, all of the cooling steps and water removal act to remove heat from the synthesis gas stream at low temperature levels. Much of this heat is simply dissipated without being recovered.
As will be discussed, the present invention, unlike the prior art related to the utilization of synthesis gas in integrated gasification combined cycles, relates to a method of generating electricity and synthesis gas in which a gas turbine is not coupled to the synthesis gas production by the use of the synthesis gas as the dominant fuel source. This allows the heat within the synthesis gas to be recovered at low temperature and transferred to the gas turbine fuel. This provides an increase in gas turbine efficiency and therefore a net cost savings.